With every breath we take we come closer to death. And if those breaths contain a good dose of polycyclic aromatic hydrocarbons, or PAHs, we may be getting to the end faster. These compounds are nasty pollutants, associated with respiratory disease, but the big concern is that several of them are known carcinogens. They are composed of carbon atoms joined together in various ring structures, very much like chicken wire. Indeed their chemistry is often referred to as chicken-wire chemistry.
So, where are these polycyclic aromatics found? Some are natural decomposition products of matter that was once alive so they occur in oil which means that anytime there is a major oil spill they can be found in the air. And should the spill be in water, as it was in the Gulf of Mexico, levels in the water rise significantly. This can affect wildlife. If oil spills into rivers or lakes that act as fresh water supply, drinking water can become contaminated. But a far bigger problem is the combustion of oil or coal, or indeed any organic matter such as meat. When such substances burn they form PAHs. Vehicle traffic, barbecue grills, cooking, tobacco smoking and wild fires all pump these compounds into the air which means we can inhale them. And of course if we eat charred foods we also ingest them. Not a good thing given their potential toxicity. Indeed, benzopyrene was the first chemical shown to be a true carcinogen.
As if it weren’t enough that PAHs are potentially carcinogenic, it turns out that they can also affect the immune system. A recent study focused on 332 children in Fresno, California where due to traffic levels of polycyclic hydrocarbons in the air are very high. Blood tests revealed that children exposed to PAHs had high levels of a class of antibodies known as IgE which our bodies originally synthesized to provide protection against parasites and allergies. Since the occurrence of parasitic infections is relatively non-existent in developed countries, IgEs found a new role in eliciting powerful inflammation reactions in response to substances the body deems to be foreign. The end result of such IgE activity is what we refer to as an allergy. Interestingly. statistics reveal that up to 70 per cent of people in Fresno have allergies.
And we are still not finished with the mischief that polycyclic aromatic hydrocarbons can cause. They may even have an epigenetic effect. Carcinogens are substances that disrupt the sequences of genes that make up DNA while substances that have an epigenetic effect do not change the basic sequence of genes, but they can make subtle changes in the structure of DNA that alters the way in which the genes are expressed. The function of genes is to produce the specific proteins the body needs and if the wrong proteins are produced, problems ensue. Polluted air, such as air containing PAHs, can have an epigenetic effect on cells that are responsible for suppressing the immune response, known as T-regulatory cells. Indeed the study in Fresno showed that children exposed to high levels of PAHs had more poorly functioning T-cell function than children exposed to low levels. In other words their bodies were more likely to produce an extreme immunological reaction such as is characteristic of asthma. The overall message here is that polycyclic aromatic hydrocarbons have no upside and should be avoided as much as possible.